The present invention pertains to organopolysiloxane gels suitable for use in cosmetic applications.
Oganopolysiloxanes have been used in numerous cosmetic applications for many years. In some of these applications, for example, organopolysiloxanes such as silicone fluids have been employed either in their native form as oils for carriers for other cosmetic ingredients, or in the form of a variety of emulsions. In many of the latter cases, a surfactant is necessary in order to keep the silicone fluid in stable suspension or dispersion. Somewhat more recently, numerous cosmetic formulations have employed creams or pastes which include organopolysiloxane gels.
U.S. Pat. No. 5,654,362 discloses silicone gels prepared by reacting a linear, Sixe2x80x94H functional polysiloxane with an xcex1,xcfx89-diene, for example 1,5-hexadiene, in the presence of a platinum hydrosilylation catalyst and a low molecular weight silicone oil. The reaction is continued until a gel is formed following which the silicone gel may be crumbled into a powder and used to thicken solvents, or by addition of further silicone oil, to form a silicone paste. The products are employed to thicken solvents such as silicone oils to a gel-like consistency. A variety of cosmetic products such as an anti-perspirants, deodorants, skin creams, etc., are disclosed. The use of highly flammable diene hydrocarbons in the preparation is a disadvantage. Moreover, creams formed from solid powders are said not to provide acceptable properties, as indicated by U.S. Pat. No. 4,980,167, wherein such formulations are said to suffer from lack of lubricity.
U.S. Pat. No. 5,859,069 discloses a gelatinous external skin treatment composition prepared from an organopolysiloxane elastomer powder having spherical particles with an average particle size of 1.0 to 15.0 xcexcm, a silicone oil, and a polyether-modified silicone. The ""069 patent indicates that prior formulations employing silicone resins are unsuitable for such uses, as they leave a filmy feeling on the skin. The polyether-modified silicone is disclosed as being absolutely necessary; and if amounts of less than 1.0% by weight are used, gelation becomes insufficient and the composition becomes unsuitable for use in cosmetics. Gelatinous external skin treatment compositions containing the spherical powder, 5-75% by weight of silicone oil, and 1-20% by weight of polyether-modified silicone are disclosed. Preparation of spherical elastomer particles is not straightforward. Moreover, the requirement for a polyether-modified silicone increases cost.
U.S. Pat. No. 5,811,487 like the ""362 patent previously disclosed, describes low molecular weight siloxane fluids thickened with silicone elastomers prepared by reaction of Sixe2x80x94H functional siloxanes and an xcex1,xcfx89-unsaturated hydrocarbon. However in the ""487 patent, the Sixe2x80x94H siloxane is first partially reacted with a monoalkenyl functionalized polyether to provide polyether functionality. The polyether-functionalized organopolysiloxane is stated to be necessary by to prepare compositions containing dispersed water, consistent with the teachings of U.S. Pat. No. 5,859,069 discussed above.
U.S. Pat. No. 5,760,116 discloses a composition containing the hydrosilylation addition product of a linear alkenyl-functionalized polyorganosiloxane and an Sixe2x80x94H functional MQ resin. Monovinyl-functional linear polyorganosiloxanes are included in exemplified formulations as alkenyl-functionalized polyorganosiloxanes in addition to divinyl-functional polyorganosiloxanes. Uniform liquid compositions formed by first preparing a gel from these ingredients, and then dispersing the gel in a further silicone having a viscosity below 1000 centistokes is disclosed. Cosmetic compositions containing these silicone compositions are also disclosed.
U.S. Pat. No. 5,854,336 discloses a process for preparing cosmetic products which involves feeding a silicone elastomer composition consisting of a silicone rubber and a carrier fluid into a reactor, mixing the composition in the reactor, delivering the composition from the reactor to a high pressure pump, and from there into a device for reducing the particles of rubber into smaller sizes. The device for reducing particle size is preferably a high pressure feed homogenizer, most preferably a sonolator. Use of high pressure pumps and devices such as sonolators increase the expense of the product.
EP 0790 055 A1 discloses compositions containing a partially reticulated elastomeric organopolysiloxane and a fatty component such as a triglyceride for use in skin care or make-up formulas. What is meant by xe2x80x9cpartially reticulatedxe2x80x9d is not defined in the specification, which refers to U.S. Pat. No. 5,266,321 for its description of suitable organopolysiloxanes.
Examples of cosmetic formulations employing silicone gels are also disclosed in International PCT Applications WO97/44010; WO98/18438; WO98/00105; WO98/00104; WO98/00103; WO98/00102, and like patents. It can be clearly seen from such patents that the range of formulations includes antiperspirants, both liquid and solid, facial creams, moisturizers, and other products. It should also be apparent from a review of these references that there are considerable differences between the variety of organosilicone gels. In particular, some of these gels provide an unacceptable oily feeling when such is not desired. Other gels are more difficult to produce, and unnecessarily increase the cost of formulation. It would be desirable to be able to produce gels in a simple fashion from well-recognized and essentially non-toxic ingredients, to produce a product which avoids the stringiness of other gels, and which can be emulsified without the use of extremely high pressure devices such as sonolators and the like.
It has now been unexpectedly discovered that organopolysiloxane gels containing a low viscosity and preferably volatile silicone oil may be easily prepared by the hydrosilylation reaction of a vinyl functional MQ resin with an Sixe2x80x94H functional poly(methylhydrogen)dimethylsiloxane in the presence of the low viscosity fluid and a small amount of platinum hydrosilylation catalyst. It has also been discovered that addition of relatively small amounts of hydrosilylation catalyst poisons such as organosulphur compounds, particularly mercaptoalkyl organopolysiloxanes, produces compositions which retain their stability over longer periods of time than when the organosulphur compounds are not employed. The resulting gels are non-stringy gels which may be easily homogenized to form a stable cream or paste without the use of high pressure or other complex mixing arrangements.
The organopolysiloxane gels of the subject invention contain a low viscosity and preferably volatile silicone oil, intimately associated with a gel matrix produced by the cross-linking of a vinyl functional MQ resin with an Sixe2x80x94H functional organopolysiloxane which contains Sixe2x80x94H functionality distributed along its backbone rather than at the termini.
The low viscosity and preferably volatile organopolysiloxane may be a low molecular weight oligomeric polydialkylsiloxane, or a cyclic siloxane. Most preferably, the low viscosity organopolysiloxane is an oligomeric polydimethylsiloxane or a cyclic polydimethylsiloxane. Other alkyl, aryl, alkaryl, and aralkyl groups are also acceptable, of course, for example, phenyl groups, benzyl groups, C1-C18 alkyl groups, and the like. However, because of cost considerations and the ease of formulation, organopolysiloxanes with methyl groups attached to the silicon atoms are highly preferred. Most preferably, the organopolysiloxanes are linear trimethylsilyl terminated polydimethylsiloxanes having on average from 2 to 50 silicon atoms in the organopolysiloxane backbone inclusive of the trimethylsilyl end groups. If volatility is desired, the number of silicon atoms should be greatly restricted, for example, to below 10, and preferably below 6. However, if relatively low viscosity but non-volatile fluids can be tolerated, extensions of the organopolysiloxane backbone to higher numbers of silicon atoms, for example, to 50 or 500 silicon atoms is possible. These non-volatile fluids should have viscosities greater than about 10 cSt, and up to about 2000 cSt. The organopolysiloxanes may also be slightly cross-linked, as long as the cross-linking does not overly increase the viscosity. Viscosity is preferably below 100 cSt, 100 cSt, more preferably below 10 cSt, and most preferably, in the case of volatile organopolysiloxanes, less than 5 cSt.
Preferably, the organopolysiloxanes are volatile organopolysiloxanes. As indicated previously, volatility can be achieved in linear organopolysiloxanes by selection of oligomeric organopolysiloxanes with at most about 6 to 10 silicon atoms in the organopolysiloxane backbone. Preferably, however, cyclic organopolysiloxanes having from 3 to 6 silicon atoms are utilized, for example, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and the like. As with the linear organopolysiloxanes, groups other than methyl groups may be present, for example, C1-C18 alkyl groups, preferably C1-4 alkyl groups, aryl groups, and the like. In addition, and also as is the case for the linear polysiloxanes, functional groups which do not interfere with the stability of the organopolysiloxane gels or with the ability to use these in cosmetic formulations may be tolerated. In particular, examples include hydroxyl (silanol) groups, alkoxy groups, for example, those which are relatively hydrolytically stable, and the like. Compounds containing reactive groups such as acetoxy groups, methoxy groups, ethoxy groups and the like, should generally be avoided unless they are retained for some special purpose in the cosmetic formulations. It is not desired to include any halo-functional compounds in the organopolysiloxane gels. Please note in this respect that minor amounts of such groups are generally unavoidable in organosiloxane resins due to their method of preparation.
A necessary component of the organopolysiloxane gel is a vinyl functional MQ resin or similar, highly crosslinked resin containing M, D, Q, and/or T moieties. Such resins are by now well-known in the art. In the organopolysiloxane art, the term xe2x80x9cresinxe2x80x9d is not applied to polymers in general, but is restricted for the use in describing relatively highly cross-linked and often relatively high molecular weight products produced by the reaction of silanes which are capable of forming three-dimensional networks. The term M refers to monofunctional units while the term Q refers to tetrafunctional units. In other words, an MQ resin contains predominantly M units wherein silicon is attached to only one oxygen in the cross-linked molecules, and SiO4/2 Q units wherein each silicon atom is attached to four other oxygen atoms, resulting in a high level of cross-linking. In many MQ resins, small amounts of difunctional R2SiO2/2 and trifunctional RSiO3/2 (D and T units, respectfully), are also present. MQ resins are frequently produced by the hydrolysis of silanes such as tetraethoxysilane, vinyldimethylethoxysilane and trimethylethoxysilane. The resulting MQ resin frequently retains some residual alkoxy functionality as a result of the method of its preparation, and will occasionally include other functionalities such as silanol functionality as well. A preferred MQ resin is MQ resin 804, available from Wacker Silicones Corporation, Adrian, Mich., which contains approximately 1.8 weight percent vinyl functionality. MQ resins having unsaturation other than vinyl, including vinyloxy, allyl, allyloxy, propenyl, etc., are less commonly available, but may be used also. The various unsaturated resins may be used alone or in admixture with other unsaturated resins.
The Sixe2x80x94H functional organopolysiloxane cross-linking agent is a necessary part of the present gel formulation. Applicants have unexpectedly discovered that when Sixe2x80x94H-terminated organopolysiloxanes are used as crosslinkers, these gels tend to have a stringy appearance. Rather, the crosslinker must be an Sixe2x80x94H functional organopolysiloxane which contains at least some Sixe2x80x94H functional units along its polymer backbone. It may or may not in addition to these Sixe2x80x94H functional units, also include terminal Sixe2x80x94H units. A preferred crosslinker is EL Crosslinker 525, a poly(methylhydrogen)dimethylsiloxane containing approximately 0.54 weight percent silicon-bonded hydrogen atoms.
The ratio of moles of unsaturation in the MQ resin to moles of Sixe2x80x94H is preferably in the range of 0.2 to 1.5, more preferably 0.3 to 1.2, and most preferably 0.4 to 0.9. Ratios of 0.85 to 0.88 have proven quite satisfactory.
A hydrosilylation catalyst is also required. Suitable hydrosilylation catalysts are well-known, and widely available from numerous sources. Preferred hydrosilylation catalysts are platinum compounds such as those disclosed in U.S. Pat. Nos. 3,159,601; 3,159,662; 3,220,972; 3,715,334; 3,775,452; and 3,814,730, and Germany published application DE 195 36176 A1, supplied in a solvent suitable for use in cosmetic formulations, such as propanediol. Other solvents may be used as well, provided that they are cosmetically acceptable, or can be removed from the gel, for example, by exposure to low pressures or stripping. The amounts of low viscosity silicone, MQ resin, and crosslinker are not critical, however, these must be present in such quantities that a stable gel is obtainable which will not separate upon standing. If too little MQ resin or too little crosslinker is used, the composition will frequently remain liquid instead of gelling. If too much crosslinker or MQ resin is obtained, a solid or crumbly gel or product will be obtained. The actual amounts can be determined by simple experimentation. Preferred compositions contain from about 60% to about 90% low viscosity organopolysiloxane, from about 5% to about 25% MQ resin, and from about 1% to about 8% Sixe2x80x94H functional crosslinker. More preferably, the compositions contain from 60 to 85% by weight volatile organopolysiloxane, 10 to 20% MQ resin, and 1 to 5% crosslinker. These percentages are percentages by weight based on the total weight of the gel.
The preparation of the gel is readily accomplished. In general, all of the ingredients except the catalyst are added and stirred slowly until a homogenous mixture is obtained, following which the catalyst is added with continual stirring. The composition can be left at room temperature until a gel is formed, or can be heated. Preferably, the composition is heated to a temperature between 70xc2x0 C. and 130xc2x0 C., more preferably between 90xc2x0 C. and 110xc2x0 C. until the mixture solidifies or gels. Gelation typically takes place within two to five hours, preferably within a maximum of about three hours, and typically within about 45 minutes. The gel is then homogenized to a smooth consistency using standard high shear mixing techniques such as the use of an Ultra-Turax(trademark) mixer or the like. High pressure mixing and recirculated mixing techniques are not necessary.
Following homogenization of the gel to a creamy consistency, numerous cosmetic ingredients can be added, such as glycerin, perfumes, emollients, lanolin, oils, pigments, U.V. absorbers, dyes, etc. Thickeners such as pyrogenic silica and other ingredients may also be added at this point to increase the viscosity of the cream to form paste-like products.
The number and type of cosmetic ingredients which may be added is not overly critical, and can be easily selected by one skilled in the art. In the application herein the term xe2x80x9ccosmetically acceptable ingredientsxe2x80x9d includes all ingredients which can be added by a cosmetic formulator which are cosmetically acceptable for use on the skin. Many such ingredients are listed in standard references, for example INTERNATIONAL COSMETIC INGREDIENT DICTIONARY AND HANDBOOK, (copyright)1997, Cosmetic, Toiletry and Fragrance Assoc., Washington, D.C.
The creamy gels of the subject invention may be used in all cosmetic formulations where silicone emulsions and other products have been used in the past, including, without limitation, skin care products such as antiperspirants, deodorants, sun care, after sun care, moisturizers, creams and lotions; color cosmetic products, such as facial powder, eye powder, eye shadow, liquid foundation, liquid-to-powder foundations, and lipsticks; and hair care products such as hair conditioners, volume enhancers, and the like.